This invention relates to a piezoelectric composite material useful as an under water acoustic transducer such as a hydrophone.
Piezoelectric composite materials are utilized as a receiver for converting an acoustic wave transmitted through water to an electric signal or as a transmitter for transmitting an acoustic wave to a water medium upon receipt of an alternate voltage of a predetermined frequency. In either utilization, it is desired that the composite material have a high under water piezoelectric constant d.sub.h since the higher d.sub.h, the better is the S/N ratio of the piezoelectric element utilizing the composite material. The constant d.sub.h is expressed by d.sub.h =d.sub.31 +2d.sub.33. Since d.sub.31 generally has a negative value, d.sub.h is increased with the increase of d.sub.33 and the decrease of .vertline.d.sub.31 .vertline. (absolute value of d.sub.31).
One known piezoelectric composite material includes a matrix of an organic polymeric material and a piezoelectric ceramic powder, such as lead zirconate titanate powder (hereinafter referred to as PZT) or lead titanate (hereinafter referred to as PT) powder, dispersed in the matrix. Since PZT powder has a large d.sub.33 and a large .vertline.d.sub.31 .vertline. while PT powder has a small d.sub.33 and a small .vertline.d.sub.31 .vertline., d.sub.h values of PZT and PT are small.